The present invention relates to a leadframe to be used for semiconductor assembly, and in particular to a leadframe of resin mold type to be used for high-speed and high heat-releasing type LSI, IC, etc.
As the method for chip packaging in semiconductor components such as LSI, IC, etc., a method to package the semiconductor chips on leadframe by resin mold or a method to package it by ceramics have been adopted in the past.
The resin mold package has high productivity of LSI and IC and it is produced at low cost and by mass production, while it is not suitable for highly heat-releasing type chips because heat-releasing property is low. Ceramic package can maintain the better characteristics of LSI and IC, while production cost is high and it is not suitable for mass production.
On the other hand, there are strong demands on small size and lightweight components in electronics industry. To cope with such demands, semiconductor package is now increasingly produced in smaller size and also with high pin count in the same size, and the manufacturing technique for such purpose has also been developed. To meet the demands for high pin count, it is necessary to shorten the distance between inner leads and to make inner lead finer and longer. However, when inner leads are made finer and longer, inner leads touch each other as they are bent during resin molding or when they are transported, and the reliability is deteriorated. For this reason, it has been customary in the past as shown in FIG. 8 to attach the tape 02 on many inner leads 01, and its strength is increased by attaching and fixing these inner leads 01. This requires, however, much labor for taping.
In this respect, a low priced resin mold package has been proposed in the Japanese Patent Publication No. 63-246851. This package is provided with the advantages of ceramic package and also maintains high-strength inner lead. This Publication discloses a multi-layer lead frame, in which the substrates consisting of polyimide film and metal plates are piled up and bonded on normal metal lead frame, and it is suitable for LSI with high heat-releasing property and high-speed type IC.
In the conventional type multi-layer leadframe, 4-10 leadframes are bonded together by continuous (serial form) side rail, and the substrates are produced independently from each other. Multi-layer leadframes are manufactured in such manner that, to each of the serial form lead frames, each substrate is bonded using adhesive or resin film having adhesives on both sides by aligning each substrate with the jig hole formed on the serial form side rail.
In the leadframe, as described in the above Patent Publication, leadframe is bonded on substrate or substrates are bonded with each other on the same plane, using double-sided adhesive tape, i.e. polyimide film coated with adhesive on both sides. This may result in the generation of gas from adhesive when it is hardened, or contaminants are increased and the reliability as package is deteriorated.
Also, resin tends to flow or withdraw poorly during molding resin sealing, and gaps are likely to occur. As the result, the air is left in the product, and productivity is deteriorated.
Further, because double-sided adhesive tape based on polyimide film is used, it is impossible to reduce the thickness of the package.
Because adhesive is coated on the entire surface of polyimide, stress is generated due to thermal expansion coefficient or thermal shrinkage of adhesive or polyimide film, and lead frame is warped or resin is cracked after packaging. The lead frame as described in the above Patent Publication or multi-layer leadframe now under development are produced by bonding a single metal material on leadframe. Because thermal behavior of adhesive, resin film having adhesive on both sides, leadframe material and metal substrate differ from each other, adhesive force is decreased during manufacturing process or leadframe may be warped.
Further, because each substrate is bonded with leadframe, it requires much labor, and also it is difficult to align lead frame with substrate. Thus, the productivity is not high.
In addition, the close fitness or sealing between metal substrate and mold resin are influenced by the stress or the shortage in resin quantity, and this results in the decline of reliability.